This invention relates to display panels for electronic devices, more specifically it relates to using multiple backlight light sources to control brightness and extend the operating life of the display panels.
Electronic devices, such as portable computers, typically have display panels with light sources that consist of a single cold-cathode fluorescent lamp (CCFL). The light from the CCFL is consolidated and channeled along a xe2x80x9clight pipexe2x80x9d behind the display panel, typically a liquid crystal display (LCD). Various mechanism in the light pipe cause the light to exit the light pipe uniformly across its surface and enter the back of the LCD, thus the CCFL are commonly known as backlight light sources. The maximum brightness of the display panel is determined in a large extent to the amount of current flowing in the CCFL light source. The brightness of the display panel can be increased or decreased by respectively increasing or decreasing the current flowing in the CCFL light source. However, there are limits on both the maximum current and minimum current that is allowed to flow into the CCFL light source. These current restrictions limit the effective range of brightness control that is achievable with a single CCFL. Consumers are demanding a larger adjustment range to allow for multiple operating environments ranging from complete darkness to full sunlight. One approach used is to provide multiple light sources to increase the brightness. However, in some electronic devices such as portable computers, additional light sources will cause the battery life to be reduced. Since the maximum brightness does not always need to be used, only one light source needs to be used to illuminate the display without producing severely non-uniform lighting. For maximum brightness operation, such as when on AC power on in full sunlight, multiple light sources can be on. One problem with exclusively selecting one light source is that the combined operating life of multiple light sources is reduced. Therefore a need exists to extend the operating life of the light sources when using multiple CCFL backlight light sources that are selectively enabled.
An electronic device has a display housing which includes a display panel and at least two light sources used to backlight the display panel. The at least two light sources are activated independently of each other to selectively increase or decrease the illumination of the display panel. A circuit is coupled to the at least two light sources. The circuit determines which of the at least two light sources is chosen such that the combined life of the at least two light sources is increased.